DESCRIPTION (Adapted from abstract): Calcium-dependent, phospholipid-binding proteins associate with biological membranes in response to cell activation and calcium entry into the cytoplasm. The goal of this project is to determine the structures and biological activities of two ubiquitous classes of these proteins, the annexins, and C2-domain containing proteins. X-ray crystallography will be used to determine the structures of annexin II, the cytoplasmic domain of synaptotagmin, and the copines. Electron microscopy of 2-dimensional crystals of these proteins on lipid monolayers will be used to determine the physical nature of the interaction of these proteins with membranes. The role of individual protein domains in promoting lipid interaction and specificity will be determined by mutagenesis of the proteins and studies on model membrane systems. Proteins that interact with and are regulated by the annexins and copines will be characterized. The localization and movements of these membrane-binding proteins in living cells and tissues will be determined. The functions of the annexins and copines will be studied by genetic silencing methods in two model organisms, the nematode C. elegans, and the ciliate Paramecium tetaurelia. These peripheral proteins are hypothesized to mediate or regulate events occurring on membrane surfaces in stimulated cells. Therefore, these studies should provide insights into basic mechanisms underlying the regulation of membrane trafficking and signal transduction across membranes occurring in normal cells and in pathological conditions including cancer, neurogenic hypertension, diabetes and other endocrine disorders.